Health threatening airborne pollutants may be subdivided into three groups; (a) airborne pathogens comprising any organism that causes disease that spreads throughout the environment via the air; (b) airborne allergens comprising any substance that, when ingested, inhaled, or touched, causes an allergic reaction and, (c) airborne volatile organic compounds (VOC) comprising any product that is designed to be sprayed at high pressure in the form of tiny particles that remain suspended in the air. The last category includes many cleaning chemicals, hair spray, various types of primer, and fuels such as gasoline and kerosene, as well as other household, beauty, or hobby products. Some fabrics, particularly those recently manufactured, also contribute to indoor airborne VOCs when they outgas, or leak out chemicals in gaseous form, over time.
Airborne pollutants can build up significantly in indoor environments with the result that the air that we breathe may become contaminated. Considering that on average humans spend approximately 90% of their time in an indoor environment, it will be appreciated that the removal of pollutants from indoor air is of importance to reduce allergies and prevent infection transmission, such as sick building syndrome.
Existing state of the art technologies for the control of airborne pathogens can be categorized as: (a) airborne trapping systems or filters, (b) airborne inactivation systems and, (c) some combination of the above.
Existing airborne inactivation technologies also include those that make use of chemicals, UV radiation and plasma discharge by-products.
Examples of chemical inactivation include the use of antimicrobial vaporizers, typically ozone or hydrogen peroxide. While these systems are effective, they are also disruptive, requiring the evacuation of indoor space to be treated and therefore are not suitable for use under normal living circumstances.
Alternative systems for the purification of air include using ultra violet light (UV) emission to kill airborne bacteria. For example, international publication No. WO 03/092751 describes a device in which a fluid (e.g. air) is passed through an array of UV lamps. In this solution the one and only inactivation mechanism is via UV radiation.
Prior art also includes the use of plasma radicals for sterilisation of air filter medium; see for example US publication No. 2004/0184972. In this document, it is proposed that an upstream plasma discharge can generate active radicals which flow upstream to a medium filter and kill any bacteria or virus trapped by the filter. However, the use of a filter medium to capture pathogens may still act as an infection reservoir and may also affect air flow stream as it gets clogged.
It is also known to use a plasma discharge which releases anti-pathogenic agents which inactivate pathogens in the air. Prior art includes methods and apparatuses for air treatment using a plasma discharge in which air is drawn around an electrode coil assembly. The plasma discharge inactivates any airborne pathogens flowing in the vicinity of the discharge. It is appreciated that the efficacy of such a device depends on the time period the pathogens and airborne pollutants are exposed to the plasma discharge and the anti-pathogenic agents generated by said device.